1. Field of the Invention
The invention relates to communication systems and more particularly to an automatic gain control method and devices for communication system receivers.
2. Description of the Related Art
Automatic gain control (AGC) is used in communication systems to maintain a constant level of output signal when the level of input signal fluctuates. The conventional AGC apparatus detects an error between the input signal level and a given target value. A feedback loop is then used to vary the attenuation factor or the gain of a variable amplifier to reduce the detected error to maintain the output signal level at the target value.
Particularly, in communication receivers, the AGC keeps the signal strength within a predefined limit. For this purpose, an adaptation algorithm can be employed to increase or decrease the gain based on the received signal power. Accordingly, the input analog signal level should be estimated to adjust the gain. Also, the adaptation process needs to converge within a short period of time as well as to provide the required accuracy for the signal level.
Existing algorithms typically use a multi-bit Analog to Digital (A/D) Converter to digitize the input signal received in analog format. The digitized signal goes through a square function and is low pass filtered. The filtered output is then squared rooted to obtain an estimate of the analog signal level. However, using multi-bit blocks such as an A/D Converter, multiplier, square root function and low pass filter, require a complex hardware implementation, increasing the cost and limiting the processing speed. Moreover, the information regarding the nature of the signal is not taken into account in estimating the analog signal level.